Acoustic noise generated from an air moving device, such as a fan assembly, is problematic in many air cooling applications. As the surrounding air temperature rises, the acoustic noise is increased due to an increase in rotation speed of a rotating assembly in the air moving device. The rotating assembly very often is coupled to a number of fan blades with fix airfoil shape. The rotation speed and airfoil shape of the fan blades determine the volume flow rate of the fluid moving device. Volume flow rate of the device is controlled by controlling the rotation speed to maintain a constant air temperature. The rotation speed is increased or decreased in response to, respectively, a rise or drop in air temperature. Such a control mechanism very often requires a control circuitry which consists of resistors, capacitors, or other types of electronic components which adds to the manufacturing cost and increases power consumption of the fluid moving device.
Therefore, it is highly beneficial to have a fluid moving device which provides low noise operation, and controls its volume flow rate with no or minimal control circuitry.